1. Field of the Invention
The present invention relates to an inkjet head operable to eject an ink onto a recording medium, for performing a printing operation on the recording medium.
2. Discussion of Related Art
There is known an inkjet head arranged, for example, in a printer, to distribute an ink supplied from an ink tank, into a plurality of pressure chambers, and to generate a drive signal in the form of a pulse train for applying a pressure to the ink stored in a selected one or ones of the pressure chambers, so that the ink is ejected through nozzle or nozzles which are held in communication with the selected pressure chamber or chambers. As means for applying the pressure to the ink stored in the selected pressure chamber or chambers, there is known an actuator unit provided by a laminar structure including a plurality of piezoelectric sheets each of which is made of a piezoelectric ceramic.
As an example of the inkjet head, U.S. Patent Application Publication No. US 2003/0156157 A1 (corresponding to JP-A-2003-311953) discloses an inkjet head equipped with an actuator unit including a common electrode, a plurality of individual electrodes and a piezoelectric sheet interposed between the common electrode and the individual electrodes. The common electrode is formed to straddle a plurality of pressure chambers. Each of the individual electrodes is provided by a main portion and an auxiliary portion which are contiguous to each other, such that the main portion is positioned to be opposed to a corresponding one of the pressure chambers, while the auxiliary portion is arranged to receive an electric voltage applied from an exterior of the inkjet head. The piezoelectric sheet has active portions each of which is interposed between the common electrode and a corresponding one of the individual electrodes so as to be polarizable in a thickness or lamination direction of the piezoelectric sheet. In operation of the inkjet head, when a predetermined level of voltage is applied between each individual electrode and the common electrode as a result of supply of a drive voltage from a flexible printed circuit (FPC), the corresponding active portion of the piezoelectric sheet is made to expand or contract in the lamination direction due to a longitudinal piezoelectric effect. The deformation of the active portion causes a volume of the corresponding pressure chamber to be changed, whereby the ink stored in the pressure chamber is pressurized to be ejected through the corresponding nozzle (which is held in communication with the pressure chamber) toward a recording medium. In the flexible printed circuit which is attached to the actuator unit, a plurality of connection pads (terminals) are provided to be connected to the individual electrodes, and drive wires are provided to connect the connection pads and output terminals of a driver IC which is operable to generate a drive voltage that is to be supplied to each of the individual electrodes.
In the inkjet head as described above, where the plurality of pressure chambers are arranged with a higher density for attending a need for improvement in printing quality and also a need for reduction in size of the inkjet head, the auxiliary portions of the individual electrodes corresponding to the plurality of pressure chambers are also necessarily disposed on the piezoelectric sheet with a higher density. The individual electrodes require to be connected at their auxiliary portions to the drive wires, through each of which the drive voltage is to be supplied to the corresponding individual electrode. There is a limitation with respect to density of the drive wires which are formed to extend from the respective connection pads in the same direction on the flexible printed circuit. It might be possible to arrange the drive wires on a plurality of flexible printed circuits rather than a single flexible printed circuit. However, this arrangement leads to an increase in a total area of the flexible printed circuits and accordingly an increase in its manufacturing cost.